1. Field of the Invention
The present invention relates to an image projecting apparatus having a variable stop and, for example, relates to an image projecting apparatus having a variable stop for dynamically changing quantity of projected light according to brightness of displayed images.
2. Description of the Related Art
U.S. Pat. No. 6,648,476 B2 ('476) suggests an image projecting apparatus for projecting an image on a display device onto a screen surface in an enlarged manner, wherein the image projecting apparatus changes the quantity of projected light through a variable stop. The image projecting apparatus adjusts a size of an effective diameter of light bundles through the variable stop for switching an image mode according to brightness and darkness of an ambient environment. This enables increasing a contrast even when the image to be projected has a lower brightness.
The image projecting apparatus suggested in '476 includes a rod integrator for uniformly illuminating an image display surface of the display device. An integrator such as the rod integrator, a lens array or the like generates plural secondary-light-source images, and light ray bundles from the plural secondary-light-source images are superimposed on one another to realize illumination with a uniform illuminance distribution. However, if aperture setting (stopping down an aperture) is performed through the variable stop, some of the plural secondary-light-source images are intercepted, thus reducing the number of secondary-light-source images passing through the variable stop due to the aperture setting. This will degrade uniform illumination effect of the integrator. Furthermore, if the aperture setting is performed through the variable stop, the F number of a projection system increases to increase a depth of focus, thereby causing dusts and the like adhered to other optical components (for example, a cover glass of the display device) near a surface conjugate with the screen to be conspicuous on a projection screen. '476 does neither recognize existence of the aforementioned problems and nor provide a countermeasure thereagainst.